Blood Gases

Blood Gases is a topic covered in the Davis's Lab & Diagnostic Tests.

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Arterial blood gases (ABGs), venous blood gases, capillary blood gases, cord blood gases.

To assess oxygenation and acid-base balance.

Patient Preparation
There are no food, fluid, activity, or medication restrictions unless by medical direction.

Normal Findings
Method: Selective electrodes for pH, Pco2, and Po2.

Blood Gas Value (pH)ArterialVenousCapillary
Birth, cord, full term7.11–7.367.25–7.457.32–7.49
Note: SI units (conversion factor × 1).
Pco2ArterialSI Units (Conventional Units × 0.133)VenousSI Units (Conventional Units × 0.133)CapillarySI Units (Conventional Units × 0.133)
Scalp40–50 mm Hg5.3–6.6 kPa
Birth, cord, full term32–66 mm Hg4.3–8.8 kPa27–49 mm Hg3.6–6.5 kPa
Newborn–adult35–45 mm Hg4.7–6 kPa41–51 mm Hg5.4–6.8 kPa26–41 mm Hg3.5–5.4 kPa
Po2ArterialSI Units (Conventional Units × 0.133)VenousSI Units (Conventional Units × 0.133)CapillarySI Units (Conventional Units × 0.133)
Scalp20–30 mm Hg2.7–4 kPa
Birth, cord, full term8–24 mm Hg1.1–3.2 kPa17–41 mm Hg2.3–5.4 kPa
0–1 hr33–85 mm Hg4.4–11.3 kPa
Greater than 1 hr–adult80–95 mm Hg10.6–12.6 kPa20–49 mm Hg2.7–6.5 kPa80–95 mm Hg10.6–12.6 kPa
HCO3-Arterial Conventional and SI UnitsVenous Conventional and SI UnitsCapillary Conventional and SI Units
Birth, cord, full term17–24 mmol/L17–24 mmol/L
2 mo–2 yr16–23 mmol/L24–28 mmol/L18–23 mmol/L
Adult22–26 mmol/L24–28 mmol/L18–23 mmol/L
O2 SatArterialVenousCapillary
Birth, cord, full term40%–90%40%–70%
Values may be at the lower end of the normal range in older adults.
Oxygen Content: ArterialOxygen Content: Venous
6.6–9.7 mmol/L 4.9–7.1 mmol/L
Tco2Arterial Conventional and SI Units mmol/LVenous Conventional and SI Units mmol/L
Birth, cord, full term13–22 mmol/L14–22 mmol/L
Adult/child22–29 mmol/L25–30 mmol/L
Base Excess ArterialConventional and SI Units
Birth, cord, full term(–10) – (–2) mmol/L
Adult/child(–2) – (+3) mmol/L

Critical Findings and Potential Interventions

Timely notification to the requesting health-care provider (HCP) of any critical findings and related symptoms is a role expectation of the professional nurse. A listing of these findings varies among facilities.

Consideration may be given to verification of critical findings before action is taken. Policies vary among facilities and may include requesting recollection and retesting by the laboratory.

Arterial Blood Gas ParameterLess ThanGreater Than
Adult/childHCO3-10 mmol/L40 mmol/L
Adult/childPco220 mm Hg (SI: 2.7 kPa)67 mm Hg (SI: 8.9 kPa)
Adult/childPo245 mm Hg (SI: 6 kPa)
NewbornsPo237 mm Hg (SI: 4.9 kPa)92 mm Hg (SI: 12.2 kPa)

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